Hasselblad 500cm - blank exposures and shutter questions

Hi Hasselblad 500cm owners. I recently acquired a 500cm and I have a couple of questions. I hope someone can enlighten me.

I developed a roll of film last night. Shots 8,9,10,11 on the roll came out blank. I started shooting on Saturday (shots 1-7). I shot 8-11 yesterday afternoon and 12 last night just to finish the roll.

I shot the whole roll sunny 16 and everything was perfectly exposed except shots 8-11 (shot yesterday) - these shots came out pure blank. I could see the image on my WLF and the shutter fired and I wound on. I can't wrap my head around what might have happened. The last shot I took at home just to finish the roll was fine.

What could I possibly have done? Is there some setting on the lens or the camera that I have fiddled with (O, T?) that could have caused this? The lens cap and dark slide were in my pocket...

My other question is about moving the shutter dial. I know to decouple the aperture and shutter dials. I am fine with doing that or setting the EV ont he lens. I can't move it past B, so I would not be able to select 1, 2, 4, 8 + seconds. I can only go to B and not beyond.

Am I missing something here or is that reserved for another system?

Is there a definitive instruction guide to using the 500?

Many thanks.

I suppose your secondary shutter could have in issue, but I think it's unlikely. Is the lens stuck on F? Theres a little button you have to press to move it.

There is no F on my lens. I have a flatter, silver 80mm planar with a V, X and M switch on the one side of the lens, another button beneath the Aperture release button (not sure what that's called) and an O and T switch on the shutter release.

Remove the back and look through it. Cock and release the shutter at all of the shutter speeds. This can tell you if the thing's working OK.
Blank frames would be from either one not opening or too high a speed with too small a stop would give.massive under exposure.